If you are using a laptop, you may run into capture issues (black screen). This is because most laptops have more than one graphics adapter. Why do they have more than one graphics adapter? Because one is used for saving power (desktop / windows), and the other is used for performance (gaming). This is done to minimize power usage on the laptop, as laptops are designed to run on batteries.
Because of this fact, it can often cause capture issues. Your laptop may be drawing one image to the power saving GPU, and another to the performance GPU. However, in order for OBS to capture efficiently, OBS itself must be running on the same GPU as that you wish to capture. If OBS is running on adapter A, and an image is being drawn on adapter B, you will get a black screen when trying to capture it.
Solution:
Go to obs executable file, and choose your graphic card
